And if quantum meant exactly that relation?

Quantum as related to quantity… in relation to Who, What, Where, When, Why…& How?

early 14c., quantite, "amount, magnitude, the being so much in measure or extent," from Old French quantite, cantite (12c., Modern French quantité) and directly from Latin quantitatem (nominative quantitas) "relative greatness or extent," coined as a loan-translation of Greek posotes (from posos "how great? how much?") from Latin quantus "of what size? how much? how great? what amount?," correlative pronominal adjective (from PIE root etymonline.com/word/*kw…, stem of relative and interrogative pronouns).

*kwo- might also be the source of: Sanskrit kah "who, which;" Avestan ko, Hittite kuish "who;" Latin quis/quid"in what respect, to what extent; how, why," qua "where, which way," qui/quae/quod "who, which;"